Method and apparatus for integration of a wireless communication system with a cable television system

ABSTRACT

The present invention is a method and apparatus for integrating a personal communication system with a cable television plant. A set of radio antenna devices (RAD) are connected to the cable plant. The RADs provide frequency conversion and power control of signal received from the cable plant for wireless transmission to the remote units. The RADs also provide power control and frequency conversion of wireless signals received from the remote units for transmission by the RADs onto the cable plant. In addition to the functions of standard base stations and centralized controller, the CATV base station must also compensate for gain variations in the cable plant. The downstream power control is regulated by a RAD reference signal which can be hidden within the CDMA signal for maximum efficiency. The upstream power control is regulated by an upstream gain reference signal which is individually transmitted by each RAD on the upstream link.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to communication systems, particularly toa method and apparatus for performing handoff between two sectors of acommon base station.

II. Description of the Related Art

In a code division multiple access (CDMA) cellular telephone, wirelesslocal loop or personal communications system, a common frequency band isused for communication with all base stations in a system. The commonfrequency band allows simultaneous communication between a remote unitand more than one base station. Signals occupying the common frequencyband are discriminated at the receiving station through the spreadspectrum CDMA waveform properties based on the use of a high speedpseudonoise (PN) code. The high speed PN code is used to modulatesignals transmitted from both the base stations and the remote units.Transmitter stations using different PN codes or PN codes that areoffset in time produce signals that can be separately received at thereceiving station. The high speed PN modulation also allows thereceiving station to receive several instances of a common signal from asingle transmitting station where the signal has traveled over severaldistinct propagation paths due to the multipath characteristics of theradio channel or purposefully introduced diversity.

The multipath characteristics of the radio channel create multipathsignals which travel several distinct propagation paths between thetransmitting station and the receiving station. One characteristic of amultipath channel is the time spread introduced in a signal that istransmitted through the channel. For example, if an ideal impulse istransmitted over a multipath channel, the received signal appears as astream of pulses. Another characteristic of the multipath channel isthat each path through the channel may cause a different attenuationfactor. For example, if an ideal impulse is transmitted over a multipathchannel, each pulse of the received stream of pulses generally has adifferent signal strength than the other received pulses. Yet anothercharacteristic of the multipath channel is that each path through thechannel may cause a different phase on the signal. For example, if anideal impulse is transmitted over a multipath channel, each pulse of thereceived stream of pulses generally has a different phase than the otherreceived pulses.

In the radio channel, the multipath is created by reflection of thesignal from obstacles in the environment, such as buildings, trees,cars, and people. In general the radio channel is a time varyingmultipath channel due to the relative motion of the structures thatcreate the multipath. For example, if an ideal impulse is transmittedover the time varying multipath channel, the received stream of pulseswould change in time location, attenuation, and phase as a function ofthe time that the ideal impulse is transmitted.

The multipath characteristics of a channel can cause signal fading.Fading is the result of the phasing characteristics of the multipathchannel. A fade occurs when multipath vectors add destructively,yielding a received signal that is smaller than either individualvector. For example if a sine wave is transmitted through a multipathchannel having two paths where the first path has an attenuation factorof X dB (decibels), a time delay of δ with a phase shift of Θ radians,and the second path has an attenuation factor of X dB, a time delay of δwith a phase shift of Θ+π radians, no signal would be received at theoutput of the channel.

In narrow band modulation systems such as the analog FM modulationemployed by conventional radio telephone systems, the existence ofmultiple path in the radio channel results in severe multipath fading.As noted above with a wideband CDMA, however, the different paths may bediscriminated at the receiving station in the demodulation process. Thediscrimination of multipath signals not only greatly reduces theseverity of multipath fading but provides an advantage to the CDMAsystem.

In an exemplary CDMA system, each base station transmits a pilot signalhaving a common PN spreading code that is offset in code phase from thepilot signal of other base stations. During system operation, the remoteunit is provided with a list of code phase offsets corresponding toneighboring base stations surrounding the base station through whichcommunication is established. The remote unit is equipped with asearching element that allows the remote unit to track the signalstrength of the pilot signal from a group of base stations including theneighboring base stations.

A method and system for providing a communication with a remote unitthrough more than one base station during the handoff process aredisclosed in U.S. Pat. No. 5,267,261, entitled "MOBILE ASSISTED SOFTHANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM," issued Nov. 30, 1993assigned to the assignee of the present invention. Using this system,communication between the remote unit and the end user is uninterruptedby the eventual handoff from an original base station to a subsequentbase station. This type of handoff may be considered as a "soft" handoffin that communication with the subsequent base station is establishedbefore communication with the original base station is terminated. Whenthe remote unit is in communication with two base stations, the remoteunit combines the signals received from each base station in the samemanner that multipath signals from a common base station are combined.

In a typical macrocellular system, a system controller may be employedto create a single signal for the other end user from the signalsreceived by each base station. Within each base station, signalsreceived from a common remote unit may be combined before they aredecoded and thus take full advantage of the multiple signals received.The decoded result from each base station is provided to the systemcontroller. Once a signal has been decoded it cannot be `combined` withother signals. Thus the system controller must select between theplurality of decoded signals produced by each base station with whichcommunication is established by a single remote unit. The mostadvantageous decoded signal is selected from among the base station andthe other signals are simply discarded.

Remote unit assisted soft handoff operates based on the pilot signalstrength of several sets of base stations as measured by the remoteunit. The Active Set is the set of base stations through which activecommunication is established. The Neighbor Set is a set of base stationssurrounding an active base station comprising base stations that have ahigh probability of having a signal strength of sufficient level toestablish communication. The Candidate Set is a set of base stationshaving a pilot signal strength at a sufficient signal level to establishcommunication.

When communications are initially established, a remote unitcommunicates through a first base station and the Active Set containsonly the first base station. The remote unit monitors the pilot signalstrength of the base stations of the Active Set, the Candidate Set, andthe Neighbor Set. When a pilot signal of a base station in the NeighborSet exceeds a predetermined threshold level, the base station is addedto the Candidate Set and removed from the Neighbor Set at the remoteunit. The remote unit communicates a message to the first base stationidentifying the new base station. A cellular or personal communicationsystem controller decides whether to establish communication between thenew base station and the remote unit. Should the cellular or personalcommunication system controller decide to do so, the cellular orpersonal communication system controller sends a message to the new basestation with identifying information about the remote unit and a commandto establish communications therewith. A message is also transmitted tothe remote unit through the first base station. The message identifies anew Active Set that includes the first and the new base stations. Theremote unit searches for the new base station transmitted informationsignal and communication is established with the new base stationwithout termination of communication through the first base station.This process can continue with additional base stations.

When the remote unit is communicating through multiple base stations, itcontinues to monitor the signal strength of the base stations of theActive Set, the Candidate Set, and the Neighbor Set. Should the signalstrength corresponding to a base station of the Active Set drop below apredetermined threshold for a predetermined period of time, the remoteunit generates and transmits a message to report the event. The cellularor personal communication system controller receives this messagethrough at least one of the base stations with which the remote unit iscommunicating. The cellular or personal communication system controllermay decide to terminate communications through the base station having aweak pilot signal strength.

The cellular or personal communication system controller upon decidingto terminate communications through a base station generates a messageidentifying a new Active Set of base stations. The new Active Set doesnot contain the base station through which communication is to beterminated. The base stations through which communication is establishedsend a message to the remote unit. The cellular or personalcommunication system controller also communicates information to thebase station to terminate communications with the remote unit. Theremote unit communications are thus routed only through base stationsidentified in the new Active Set.

Because the remote unit is communicating with the end user though atleast one base station at all times throughout the soft handoff process,no interruption in communication occurs between the remote unit and theend user. A soft handoff provides significant benefits in its inherent"make before break" communication over conventional "break before make"techniques employed in other cellular communication systems.

In a cellular or personal communication telephone system, maximizing thecapacity of the system in terms of the number of simultaneous telephonecalls that can be handled is extremely important. System capacity in aspread spectrum system can be maximized if the transmission power ofeach remote unit is controlled such that each transmitted signal arrivesat the base station receiver at the same level. In an actual system,each remote unit may transmit the minimum signal level that produces asignal-to-noise ratio that allows acceptable data recovery. If a signaltransmitted by a remote unit arrives at the base station receiver at apower level that is too low, the bit-error-rate may be too high topermit high quality communications due to interference from the otherremote units. On the other hand, if the remote unit transmitted signalis at a power level that is too high when received at the base station,communication with this particular remote unit is acceptable but thishigh power signal acts as interference to other remote units. Thisinterference may adversely affect communications with other remoteunits.

Therefore to maximize capacity in an exemplary CDMA spread spectrumsystem, the transmit power of each remote unit within the coverage areaof a base station is controlled by the base station to produce the samenominal received signal power at the base station. In the ideal case,the total signal power received at the base station is equal to thenominal power received from each remote unit multiplied by the number ofremote units transmitting within the coverage area of the base stationplus the power received at the base station from remote units in thecoverage area of neighboring base stations.

The path loss in the radio channel can be characterized by two separatephenomena: average path loss and fading. The forward link, from the basestation to the remote unit, operates on a different frequency than thereverse link, from the remote unit to the base station. However becausethe forward link and reverse link frequencies are within the samegeneral frequency band, a significant correlation between the averagepath loss of the two links exists. On the other hand, fading is anindependent phenomenon for the forward link and reverse link and variesas a function of time.

In an exemplary CDMA system, each remote unit estimates the path loss ofthe forward link based on the total power at the input to the remoteunit. The total power is the sum of the power from all base stationsoperating on the same frequency assignment as perceived by the remote inunit. From the estimate of the average forward link path loss, theremote unit sets the transmit level of the reverse link signal. Shouldthe reverse link channel for one remote unit suddenly improve comparedto the forward link channel for the same remote unit due to independentfading of the two channels, the signal as received at the base stationfrom this remote unit would increase in power. This increase in powercauses additional interference to all signals sharing the same frequencyassignment. Thus a rapid response of the remote unit transmit power tothe sudden improvement in the channel would improve system performance.Therefore it is necessary to have the base station continuallycontribute to the power control mechanism of the remote unit.

Remote unit transmit power may also be controlled by one or more basestations. Each base station with which the remote unit is incommunication measures the received signal strength from the remoteunit. The measured signal strength is compared to a desired signalstrength level for that particular remote unit. A power adjustmentcommand is generated by each base station and sent to the remote unit onthe forward link. In response to the base station power adjustmentcommand, the remote unit increases or decreases the remote unit transmitpower by a predetermined amount. By this method, a rapid response to achange in the channel is effected and the average system performance isimproved. Note that in a typical cellular system, the base stations arenot intimately connected and each base station in the system is unawareof the power level at which the other base stations receive the remoteunit's signal.

When a remote unit is in communication with more than one base station,power adjustment commands are provided from each base station. Theremote unit acts upon these multiple base station power adjustmentcommands to avoid transmit power levels that may adversely interferewith other remote unit communications and yet provide sufficient powerto support communication from the remote unit to at least one of thebase stations. This power control mechanism is accomplished by havingthe remote unit increase its transmit signal level only if every basestation with which the remote unit is in communication requests anincrease in power level. The remote unit decreases its transmit signallevel if any base station with which the remote unit is in communicationrequests that the power be decreased. A system for base station andremote unit power control is disclosed in U.S. Pat. No. 5,056,109entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN ACDMA CELLULAR MOBILE TELEPHONE SYSTEM," issued Oct. 8, 1991, assigned tothe Assignee of the present invention.

Base station diversity at the remote unit is an important considerationin the soft handoff process. The power control method described aboveoperates optimally when the remote unit communicates with each basestation through which communication is possible. In doing so, the remoteunit avoids inadvertently interfering with communications through a basestation receiving the remote unit's signal at an excessive level butunable to communicate a power adjustment command to the remote unitbecause communication is not established therewith.

A typical cellular or personal communication system contains some basestations having multiple sectors. A multi-sectored base stationcomprises multiple independent transmit and receive antennas. Theprocess of simultaneous communication with two sectors of the same basestation is called softer handoff. The process of soft handoff and theprocess of softer handoff are the same from the remote unit'sperspective. However the base station operation in softer handoff isdifferent from soft handoff. When a remote unit is communicating withtwo sectors of the same base station, the demodulated data signals ofboth sectors are available for combination within the base stationbefore the signals are passed to the cellular or personal communicationsystem controller. Because the two sectors of a common base stationshare circuitry and controlling functions, a variety of information isreadily available to sectors of a common base station that is notavailable between independent base stations. Also two sectors of acommon base station send the same power control information to a remoteunit (as discussed below).

The combination process in softer handoff allows demodulated data fromdifferent sectors to be combined before decoding and thus produce asingle soft decision output value. The combination process can beperformed based on the relative signal level of each signal thusproviding the most reliable combination process.

As noted above, the base station can receive multiple instances of thesame remote unit signal. Each demodulated instance of the arrivingsignal is assigned to a demodulation element. The demodulated output ofthe demodulation element is combined. The combined signal is decoded.The demodulation elements, instead of being assigned to a single sector,may be assigned to a signal from any one of a set of sectors in the basestation. Thus, the base station may use it resources with highefficiency by assigning demodulation elements to the strongest signalsavailable.

Combining signals from sectors of a common base station also allows asectorized base station to make a single power adjustment command forremote unit power control. Thus the power adjustment command from eachsector of a common base station is the same. This uniformity in powercontrol allows flexible handoff operation in that sector diversity atthe remote unit is not critical to the power control process. Furtherdetails of the softer handoff process are disclosed in U.S. patentapplication Ser. No. 08/144,903, filed Oct. 30, 1993, entitled "METHODAND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASESTATION," assigned to the assignee of the present invention. Furtherinformation on the benefits and application of softer handoff aredisclosed in U.S. patent application Ser. No. 08/144,901, filed Oct. 30,1993, entitled "METHOD AND APPARATUS FOR REDUCING THE AVERAGE TRANSMITPOWER FROM A SECTORIZED BASE STATION" and U.S. patent application Ser.No. 08/316,155, filed Sep. 30, 1994 entitled "METHOD AND APPARATUS FORREDUCING THE AVERAGE TRANSMIT POWER OF A BASE STATION" each of which isassigned to the assignee of the present invention.

Each base station in the cellular system has a forward link coveragearea and a reverse link coverage area. These coverage areas define thephysical boundary beyond which base station communication with a remoteunit is degraded. In other words, if a remote unit is within the basestation's coverage area, the remote unit can communicate with the basestation, but if the remote unit is beyond the coverage area,communications are compromised. A base station may have single ormultiple sectors. Single sectored base stations have approximately acircular coverage area. Multi-sectored base stations have independentcoverage areas that form lobes radiating from the base station.

Base station coverage areas have two handoff boundaries. A handoffboundary is defined as the physical location between two base stationswhere the link would perform the same regardless of whether the remoteunit were communicating with the first or second base station. Each basestation has a forward link handoff boundary and a reverse link handoffboundary. The forward link handoff boundary is defined as the locationwhere the remote unit's receiver would perform the same regardless ofwhich base station it was receiving. The reverse link handoff boundaryis defined as the location of the remote unit where two base stationreceivers would perform the same with respect to that remote unit.

Ideally these boundaries should be balanced, meaning that they shouldhave the same physical location. If they are not balanced, systemcapacity may be reduced as the power control process is disturbed or thehandoff region unreasonably expands. Note that handoff boundary balanceis a function of time, in that the reverse link coverage area shrinks asthe number of remote units present therein increases. Reverse linkpower, which increases with each additional remote unit, is inverselyproportional to the reverse link coverage area. An increase in receivepower decreases the effective size of the reverse link coverage area ofthe base station and causes the reverse link handoff boundary to moveinward toward the base station.

To obtain high performance in a CDMA or other cellular system, it isimportant to carefully and accurately control the transmit power levelof the base stations and remote units in the system. Transmit powercontrol limits the amount of self-interference produced by the system.Moreover, on the forward link, a precise level of transmit power canserve to balance the forward and reverse link handoff boundaries of abase station or a single sector of a multi-sectored base station. Suchbalancing helps to reduce the size of the handoff regions, increaseoverall system capacity, and improve remote unit performance in thehandoff region.

Before adding a new base station to the existing network, the forwardlink (i.e. transmit) power and the reverse link (i.e. receive) signalpower of the new base station are both approximately equal to zero. Tobegin the process of adding the new base station, an attenuator in thereceive path of the new base station is set to a high attenuation level,creating a high level of artificial noise receive power. An attenuatorin the transmit path is also set to a high attenuation level, which inturn causes a low transmit power level. The high level of artificialnoise receive power results in the reverse link coverage area of the newbase station being very small. Similarly, because the forward linkcoverage area is directly proportional to the transmit power, the verylow transmit power level and the forward link coverage area is also verysmall.

The process then continues by adjusting the attenuators in the receiveand transmit paths in unison. The attenuation level of the attenuator inthe receive path is decreased, thereby decreasing the level ofartificial noise receive power, increasing the natural signal level, andhence increasing the size of the reverse link coverage area. Theattenuation level of the transmit path attenuator is also decreased,thereby increasing the transmit power level of the new base station andexpanding its forward link coverage area. The rate at which the transmitpower is increased and the artificial noise receive power is decreasedmust be sufficiently slow to permit handoff of calls between the new andsurrounding base stations as the new base station is added to or removedfrom the system.

Each base station in the system is initially calibrated such that thesum of the unloaded receiver path noise and the desired pilot power isequal to some constant. The calibration constant is consistentthroughout the system of base stations. As the system becomes loaded(i.e. remote units begin to communicate with the base stations), acompensation network maintains the constant relationship between thereverse link power received at the base station and the pilot powertransmitted from the base station. The loading of a base stationeffectively moves the reverse link handoff boundary closer in toward thebase station. Therefore to imitate the same effect on the forward link,the pilot power is decreased as loading is increased. The process ofbalancing the forward link handoff boundary to the reverse link handoffboundary is referred to as base station breathing is detailed in U.S.Pat. No. 5,548,812 entitled "METHOD AND APPARATUS FOR BALANCING THEFORWARD LINK HANDOFF BOUNDARY TO THE REVERSE LINK HANDOFF BOUNDARY IN ACELLULAR COMMUNICATION SYSTEM" issued Aug. 20, 1996 and assigned to theassignee of the present invention. The process of balancing the forwardlink handoff boundary to the reverse link handoff boundary during theaddition or removal of a base station from a system is referred to asbase station blossoming and wilting is detailed in U.S. Pat. No.5,475,870 entitled "APPARATUS AND METHOD FOR ADDING AND REMOVING A BASESTATION FROM A CELLULAR COMMUNICATION SYSTEM" issued Dec. 12, 1995 andassigned to the assignee of the present invention.

It is desirable to control the relative power used in each forward linksignal transmitted by the base station in response to controlinformation transmitted by each remote unit. The primary reason forproviding such control is to accommodate the fact that in certainlocations the forward link may be unusually disadvantaged. Unless thepower being transmitted to the disadvantaged remote unit is increased,the signal quality may become unacceptable. An example of such alocation is a point where the path loss to one or two neighboring basestations is nearly the same as the path loss to the base stationcommunicating with the remote unit. In such a location, the totalinterference would be increased by three times over the interferenceseen by a remote unit at a point relatively close to its base station.In addition, the interference coming from the neighboring base stationsdoes not fade in unison with the signal from the active base station aswould be the case for interference coming from the active base station.A remote unit in such a situation may require 3 to 4 dB of additionalsignal power from the active base station to achieve adequateperformance.

At other times, the remote unit may be located where thesignal-to-interference ratio is unusually good. In such a case, the basestation could transmit the corresponding forward link signal using alower than nominal transmitter power, reducing interference to othersignals being transmitted by the system.

To achieve the above objectives, a signal-to-interference measurementcapability can be provided within the remote unit receiver. Asignal-to-interference measurement is performed by comparing the powerof the desired signal to the total interference and noise power. If themeasured ratio is less than a predetermined value, the remote unittransmits a request to the base station for additional power on theforward link. If the ratio exceeds the predetermined value, the remoteunit transmits a request for power reduction. One method by which theremote unit receiver can monitor signal-to-interference ratios is bymonitoring the frame error rate (FER) of the resulting signal.

The base station receives the power adjustment requests from each remoteunit and responds by adjusting the power allocated to the correspondingforward link signal by a predetermined amount. The adjustment wouldusually be small, typically on the order of 0.5 to 1.0 dB, or around12%. The rate of change of power may be somewhat slower than that usedfor the reverse link, perhaps once per second. In the preferredembodiment, the dynamic range of the forward link adjustment istypically limited such as from 4 dB less than nominal to about 6 dBgreater than nominal transmit power.

CDMA base stations have the ability to provide accurate control overtheir transmit power level. To provide accurate power control, it isnecessary to compensate for variations in the gain in the variouscomponents comprising the transmit chain of the base station. Variationsin the gain typically occur over temperature and aging such that asimple calibration procedure at deployment does not guarantee a preciselevel of output transmit power over time. Variations in the gain can becompensated by adjusting the overall gain in the transmit chain so thatthe actual transmit power of the base station matches a calculateddesired transmit power. Each base station sector produces severalsignaling channels which operate at a variety of data rates and relativesignal levels which combined create a raw radio frequency transmitsignal. The channel element modulators, each of which corresponds to achannel, calculate the expected power of each channel signal. The basestation also comprises a base station transceiver system controller(BTSC) which generates a desired output power of the sector by summingthe expected powers of each channel.

A key aspect in implementing a wireless communication system isplacement of antennas throughout the coverage area such that everylocation in the entire coverage area where a remote unit may be locatedis supported with sufficient signal levels. To create a distributedantenna, the transmit output of the base station is fed to a string ofantenna elements each separated by delay. A distributed antenna exploitsthe ability of direct sequence CDMA to discriminate against multipath bycreation of deliberate multipath that satisfies discrimination criteria.

A technique for improving performance of a distributed antenna systemusing parallel strings of discrete antennas wherein each antenna on acommon string is separated from its neighbors by delay is disclosed inU.S. Pat. No. 5,280,472 entitled "CDMA MICROCELLULAR TELEPHONE SYSTEMAND DISTRIBUTED ANTENNA SYSTEM THEREFOR", which issued as on Jan. 18,1994 and assigned to the assignee of the present invention. Furtherdevelopment of the distributed antenna concept is disclosed in U.S.patent application Ser. No. 08/112,392, filed Aug. 27, 1993, entitled"DUAL DISTRIBUTED ANTENNA SYSTEM", and assigned to the assignee of thepresent invention. In the distributed antenna arrangement, signalstransmitted from antennas of different antenna elements at a common nodeare provided different delay paths between the base station and theantenna. The antenna elements may comprise downconversion circuitry thusreducing the cabling path loss between the antenna elements and the basestation and allowing the use of readily available SAW devices as delayelements.

Another advantage of the distributed antenna arrangement is that littlesite specific engineering is required for installation. Normally,antenna placement is determined only by physical constraints, togetherwith the requirement that every location desiring service must becovered by a set of two antennas. There is no concern for theoverlapping of antenna patterns. In fact, overlapping coverage isdesirable in that it provides diversity operation to all terminals inthe overlap area. Overlap is, however, not required.

An objective of a personal mobile communications network is to providecoverage over a large geographic region. Such broad geographic coverageis essential and must be provided on the first day of service to attractusers in the present economic environment. One of the major expenses ofproviding coverage over a large geographic area is the acquisition ofreal estate and land usage rights and the installation of base stationseach providing coverage for a portion of the total geographic coveragearea.

Note that cable television (CATV) networks provide extensive coverageover nearly all suburban areas. Thus if the CATV network, called thecable plant, could be used as the basis for a wireless communicationnetwork, the task of obtaining real estate and land usage rights and theexpense of installing discrete base stations could be avoided. Thus acentralized headend processor could provide the necessary signalprocessing functions at a single location within the geographic regionand the cable distribution means could be used to carry the wirelesssignal to the users.

The characteristics of the CDMA system provide a myriad of advantages ina CATV based wireless system. The integration of the wirelesscommunication network with the cable plant can be carefully orchestratedto take full benefit of the flexibility and capacity of the CDMA system.The present invention seeks to define such a system.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for integrating apersonal communication system with a cable television plant. A set ofradio antenna devices (RADs) are connected to the cable plant. The RADsprovide frequency conversion and power control of the signal receivedfrom the cable plant for wireless transmission to the remote units. TheRADs also provide power control and frequency conversion of wirelesssignals received from the remote units for transmission by the RADs ontothe cable plant.

At the headend of the cable plant, a base station is installed to act asan interface between the RADs and the public switch telephone network(PSTN). The base station provides the functions of a standardmacrocellular base station such as frequency downconversion,demodulation, signal combination, and signal decoding as well asmodulation, power control and frequency upconversion. The base stationmay also perform some of the functions which are usually performed by acentralized system controller in a standard macrocellular system such asselection vocoding functions.

In addition to the functions of standard base stations and centralizedsystem controller, the CATV base station must also compensate for gainvariations in the cable plant. The downstream power control is regulatedby a RAD reference signal which can be hidden within the CDMA signal formaximum efficiency. The upstream power control is regulated by anupstream gain reference signal which is individually transmitted by eachRAD on the upstream link.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a diagram illustrating an exemplary cable plant;

FIG. 2 is a block diagram illustrating an exemplary cable plantintegrated with a personal communication system;

FIG. 3 shows the forward link signal processing structure of anexemplary radio antenna device (RAD);

FIG. 4 shows the reverse link signal processing structure of anexemplary RAD;

FIG. 5 shows an antenna pattern of a typical three sectored basestation;

FIG. 6 shows a set of distributed antennas providing coverage to aconcentrated coverage area;

FIG. 7 illustrates an exemplary embodiment of a standard cellular systemshowing three single sectored base stations;

FIG. 8 illustrates an exemplary embodiment of a three sectored basestation of a standard cellular system;

FIG. 9A is an exemplary spectral distribution on the downstream cableplant link;

FIG. 9B is an exemplary spectral distribution on the upstream cableplant link;

FIG. 10 illustrates an exemplary block diagram of a base station inaccordance with the present invention;

FIG. 11 shows a scenario in which the RAD reference signal is placed inthe center of the CDMA sector signal; and

FIG. 12 is a block diagram illustrating partially the functions of thedigital shelves.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary cable plant. Satellite signal antennas 10 and12 receive television (T.V.) signals typically in the Ku or C bandfrequency range at headend 4. T.V. receiver 14 within headend 4 convertsthe signals to the lower RF frequencies for transmission throughout thecable plant. Typically downstream T.V. signals are carried within thefrequency range of 54 MegaHertz (MHz) to 550 MHz. The electrical RFsignals output from T.V. receiver 14 are passed to a bank of electricalto optical signal converters 16A-16I. Each of electrical to opticalsignal converters 16A-16I converts the electrical RF signals to opticalsignals for fiber optic transmission to a subset of the geographicalcoverage areas serviced by a plurality of fiber nodes 20A-20I. Forexample, fiber 2 carries the optical signals from electrical to opticalsignal converter 16A to fiber node 20A. Fiber nodes 20A-20I are spacedthroughout the geographic area serviced by the signal from fiber 2. Eachof fiber nodes 20A-20I provides the signal through electrical signalcable to a plurality of destinations 24A-24I, such as houses, apartmentbuildings, and businesses. Located along the length the electricalsignal cable are a plurality of bi-directional amplifiers 22A-22I. Theelectric signal cable and amplifiers may also be arranged in a paralleland/or star configuration rather than the series configuration shown inFIG. 1.

The path of the T.V. signal from headend 4 to destinations 24A-24I isreferred to as the downstream path. Typically a city with a populationof about 1 million people has three or four headends. The fiber lines,such as fiber 2, run long distances in underground conduits or aboveground poles. From each fiber node 20A-20I, the electric signal cablesusually run about a mile or less depending on the number of destination.Bi-directional amplifiers 22A-22I may be inserted every 1000 feet alongthe electrical signal cable. Typically no more than five bi-directionalamplifiers are cascaded along any one electrical signal cable due to theintermodulation distortion added by each amplifier.

The Federal Communication Commission (FCC) regulations require that thecable plant provide bidirectional communication with the destinations.As such, in addition to the downstream system providing T.V. signals tothe destination, an upstream system provides a signaling path fromdestinations 24A-24I back to headend 4. The upstream path is intended tocarry a much lower volume of signaling traffic than the downstream path.The upstream path may be used, for example, to indicate the selection ofa "pay-per-view" option by a user.

The upstream link operates essentially the same as the reverse of thedownstream link. Typically the upstream link operates on a more limitedfrequency range such as from 5-40 MHz. Signals from destinations 24A-24Iare carried via the electrical signal cable and bi-directionalamplifiers 22A-22I to fiber node 20A. At fiber nodes 20A-20I, thesignals are converted from the electrical form to optical form fortransmission on fiber 2. At headend 4, the upstream signals areconverted to electrical form by optical to electrical signal converters18A-18I. The upstream signal are then processed by user signal processor6.

In typical configurations, there is a one to one mapping betweenelectrical to optical signal converters 16A-16I and fiber nodes 20A-20I.A unique fiber within fiber 2 carries each downstream and upstreamsignal separately.

FIG. 2 shows an exemplary architecture embodying the present inventionintegrated with the exemplary cable plant of FIG. 1. Headend 4 has beenreplaced with headend 40 which provides the wireless communicationfunctionality. Within headend 40 is base station 44 which interfaces thewireless communication network with public switched telephone network(PSTN) 30. In addition base station 44 provides for the generation ofthe forward link code division multiple access (CDMA) call signals aswell as pilot and other overhead signals which are distributed on thedownstream link. Base station 44 also provides for the selection orcombination of the reverse link CDMA call signal and overhead signals asreceived on the upstream link. Base station 44 is explained in greaterdetail subsequently herein.

As noted above, the downstream CATV plant typically carries T.V. signalsin a frequency band of 54 MHz-550 MHz. However the downstream CATV plantis capable of providing communication of signals up to 700 MHz. Somevery new systems are capable of operation up to 850 MHz. In those oldersystems that run only to 350 to 450 MHz, several T.V. may need to becleared for use in by the PCS. In the preferred embodiment of thepresent invention, the CDMA forward links signals are carried in the 550MHz-700 MHz frequency range. Each sector of the CDMA forward link isallocated a portion of the available frequency band within the CATVplant. The forward link output from base station 44 is summed with theT.V. signals from T.V. receiver 14 by summer 42. The forward link CDMAsignals are transmitted in essentially the same manner as the T.V.signals through the downstream CATV link. As explained in great detailsubsequently herein, the destination of some of the forward link CDMAsignals are the radio antenna devices (RAD) 50A-50I. RADs 50A-50Iradiate the forward link CDMA signal into the geographic service areaassociated with fiber node 20A. RADs 50A-50I are spaced along the lengthof electrical cable associated with fiber node 20A typically with aspacing of 1000-1500 feet. The forward link CDMA signals are passedthrough bi-directional amplifiers 22A-22I with the T.V. signals. RADs50A-50I, obviously, must be placed such that the signals they providemay be radiated with sufficient energy levels over the desired coveragearea. As such, if the electrical cable associated with fiber node 20A isunderground, RADs 50A-50I may be installed at one or more ofdestinations 24A-24I. For example, even if the electrical cable isunderground, the cable emerges from the ground to connect to thephysical structure associated with each destination. RADs 50A-50I may beinstalled on the roof top of a residence. If the electrical cableassociated with fiber node 20 is above ground, RADs 50A-50I may beplaced anywhere along the cable itself or with one of the polessupporting the electrical cable.

As noted above the upstream link operates over the frequency range of5-40 MHz. The reverse link CDMA system operates most advantageously ifthere is diversity in the receive path such that each of RADs 50A-50Ihas two different receive antennas each providing a separate signal backto base station 44. Thus if the reverse link CDMA signals were to befrequency multiplexed within the CATV plant, twice as much spectrumbandwidth would be required on the reverse link than that used for theforward link CDMA signals. But only 35 MHz of bandwidth is available onthe upstream CATV plant. Thus, as shown in FIG. 2, each fiber node20A-20I corresponds to a direct path to a corresponding one of opticalto electrical signal converters 18A-18I. Each of optical to electricalsignal converters 18A-18I is connected to headend processor 40. Basestation 44 outputs and receives signal to and from PSTN 30.

As noted above, one important aspect of a CDMA communication system isthe power control of both the forward and reverse link. In prior artCDMA base stations, the signal generation means and the antenna meansare collocated. Thus the prior CDMA base stations may simply set thetransmit power level directly. Likewise, the prior art CDMA basestations may directly measure the signal levels of the signals itreceives.

In contrast, in the CATV plant based system, base station 44 and RADs50A-50I can be located many miles apart. Also, a quick glance at FIG. 2shows that the path between each individual RAD 50A-50I to base station44 is different. In addition to the fixed physical differences betweenthe paths, the gain of the CATV plant varies considerably over time suchas in response to the wide range of temperatures over which the systemmust work. The CATV plant also is subjected to a variety of dynamicingress signals. Ingress signals are unwanted signals which enter thecable plant. A multitude of ingress signals are created in the urbanenvironment such as from other communications system (such as local T.V.systems, commercial broadcast radio systems, Citizen Band Radios) andfrom machinery which creates random sporadic emissions (such asemissions from starting an automobile). The ingress signals are highlyunpredictable and highly variable over time.

Given the importance of power control to the CDMA system and thecomplexity and variability of the amplitude response of the cable plant,power control becomes an important aspect of the present invention. Theforward link power control compensation is accomplished by use of a RADreference signal transmitted over the downstream link. The reverse linkpower control compensation is accomplished by use of an upstream gainreference signal transmitted over the upstream link. The form andfunction of the RAD reference signal and upstream gain reference signalare explained explicitly below.

Before explaining the power control compensation mechanism, first let usexamine the structure of the RADs themselves. Each RAD provides bothforward link and reverse link signal processing. FIG. 3 shows theforward link signal processing structure of an exemplary RADincorporating the preferred embodiment thereof. In FIG. 3, coupler 60couples the RF signal from the electrical cable. Splitter 62 divides theincoming signal so that it can be used by two different processingelements. RAD reference signal processor 84 extracts the RAD referencesignal from the variety of signals present on the electrical cable. TheRAD reference signal has three purposes: to act as a channel gainreference, to act as a reference for the frequency synthesizers, and totransmit control data to the RAD. Each of these functions is detailedbelow. RAD reference signal processor 84 extracts the frequencyreference signal from the RAD reference signal and provides it to phaselock loops (PLL) 64 and 68. RAD reference signal processor 84 alsoextracts the gain reference signal which is further processed by RADmicroprocessor 88 and eventually provided to gain control 72. RADreference signal processor 84 further extracts any control data andprovides it to RAD microprocessor 88 for further analysis. The controldata may comprise commands from headend 40 intended solely for this RAD.For example, the control data may indicate that the frequency of PLL 68or PLL 64 should be changed to a new frequency.

Intermediate frequency (IF) processor 70 also receives a signal fromsplitter 62. IF processor 70 frequency converts the incoming signal suchthat the desired signal is centered about a predetermined IF frequency.As noted above, the forward link CDMA signals are frequency multiplexedin the cable plant. The frequency generated by PLL 64 is mixed with theincoming signal from splitter 62 such that the desired waveform iscentered about the predetermined IF frequency. Typically a IF processor70 uses a surface acoustic wave (SAW) filter or other filter matched tothe wave shape of the signal which the RAD is transmitting and rejectingthe other signals coming from splitter 62. If the physical distancebetween the RADs is insufficient to provide delay to create usablemultipath delays, IF processor 70 may also comprise a field replaceableor programmable or fixed delay element.

The IF frequency signal is output from IF processor 70 to gain control72. Gain control 72 sets the transmit output power of the RAD inresponse to a control signal from RAD microprocessor 88. Mixer 74upconverts the gain controlled signal output from gain control 72 to thetransmission frequency. Power amplifier 76 provides a nominally fixedgain and amplifies the signal to an appropriate power for transmission.Filter 77 filters the signal for transmission to suppress any unwantedmixer products. Coupler 78 couples a small amount of the powertransmitted from this RAD over antenna 80. The coupled power fromcoupler 78 is measured by power detector 90 and the result is reportedback to RAD microprocessor 88.

FIG. 4 shows the reverse link signal processing structure of anexemplary RAD incorporating the preferred embodiment thereof. In FIG. 4,antennas 100 and 126 are each associated with this RAD. Using twocollocated antennas placed some distance apart at each RAD introducesdesirable diversity. The separation between the antennas should allowthe two antennas to have substantially the same coverage area whileproviding independent fading. Placing two antennas at one base stationto obtain diversity is common practice in macrocellular systems. In amacrocellular system, two antennas having relatively large coverageareas, generally on the order of several miles, are placed at one basestation. Typically the antennas are placed about 5 to 20 wavelengthsapart to obtain path diversity and independence in fading. As notedabove, to achieve the full benefit from path diversity, each diversesignal is separately demodulated before the resulting demodulatedsignals are summed together to produce an aggregate result. Thedemodulation process is performed in headend 40. Thus in the presentinvention two separate receive signals are transported from each RADback to headend 40, one corresponding to each of antennas 100 and 126referred to respectively as the alpha and beta signal paths. Theupstream signaling in the cable plant thus requires approximately twicethe bandwidth that is required by the downstream signaling.

From antenna 100, the alpha receive signal enters controllableattenuator 102 and from antenna 126 the beta receive signal enterscontrollable attenuator 128. Although the placement of controllableattenuators 102 and 128 directly after antennas 100 and 126 seemscounter-intuitive, controllable attenuators 102 and 128 serve twoimportant functions. In order for the signal demodulated at headend 40to be properly combined, the relative signal levels of each signal to becombined must be known so that the signal can be properly weighted forcombination with the others. Because only one upstream gain referencesignal is generated to facilitate this process from each RAD, theupstream gain reference signal is used to indicate the relative level ofboth of the two received signals from a single RAD. Thus the two pathsmust be balanced in that they both provide the same receive performance(noise figure and gain) to the signals they receive. Controllableattenuators 102 and 128 may be used to calibrate the alpha and betapaths.

The second purpose of controllable attenuators 102 and 128 is toimplement RAD breathing and blossoming. Breathing is a process by whichthe forward and reverse link handoff boundaries are balanced withrespect to neighboring RADs. Blossoming is the process by which RADs areadded or removed from operation. RAD microprocessor 88 controls theattenuation of controllable attenuators 102 and 128 to effect theseprocesses. Both breathing and blossoming including a variety ofimplementation variations are explained in detail in above-mentionedU.S. Pat. Nos. 5,548,812 and 5,475,870.

Next within each path, the receive signal is amplified by low noiseamplifier 104 and 130. The amplified signal is then converted to a fixedIF frequency by mixer 106 and 132. The fixed IF remains at the samefrequency regardless of the frequency being received by antennas 100 and126 and the frequency used to transmit the signal from the RAD toheadend 40 over the cable plant. Mixers 106 and 132 are driven by PLL118 which produces a frequency as programmed by RAD microprocessor 88and with reference to RAD reference signal (connections not shown forclarity.)

The output of mixers 106 and 132 is bandpass filtered by filters 108 and134 respectively to reject unwanted frequencies. Time delay units 110and 136 may be fixed, field replaceable or controllable delayprovisions. A need may arise to provide delay in the receive chain if,for instance, the two signal paths from each antennas 100 and 126 arecombined or if the signals are combined with signals from other RADs inthe cable plant. For more information see the above-mention U.S. Pat.No. 5,280,472 and U.S. patent application Ser. No. 08/112,392.

Mixer 112 converts the alpha signal to the proper frequency fortransmission over the cable plant using a mixing signal provided by PLL120. Mixer 138 converts the beta signal to the proper frequency fortransmission over the cable plant using a mixing signal provided by PLL122. PLLs 120 and 122 are programmed by RAD microprocessor 88 andreferenced to RAD reference signal (connections not shown for clarity.)Summer 144 sums together on a common output the alpha and beta signalsand the upstream gain reference signal. Gain control 146 adjusts thegain of the combined signal and amplifier 148 amplifies the combinedsignal. Coupler 150 couples the combined signal onto the cable plant.

In FIG. 4 RAD microprocessor 88 is shown again for clarity. In thepreferred embodiment RAD microprocessor 88 is a single processing unitthat provides control over both the receive and transmit portions of theRAD. Also shown in FIG. 4 is voltage controlled temperature compensatedcrystal oscillator (VCTCXO) 154. VCTCXO 154 provides a clock signal forRAD microprocessor 88 and a reference signal for upstream gain referencesignal generation 152. RAD microprocessor 88 can synchronize and/orphase lock the output of VCTCXO 154 with RAD reference signal after theRAD reference signal becomes available. When the RAD first receivespower, the output of VCTCXO 154 can provide a clock and references bywhich bootstrapping functions can be achieved.

Upstream gain reference signal generation 152 provides a power controlmechanism for the RAD. Each RAD transmits a distinguishable upstreamgain reference signal back to headend 40 where the signal is measuredand compared to the other upstream gain reference signal levelsreceived. Headend 40 can send a message via the RAD reference signal tothe individual RAD directing it to increase or decrease power level ofthe signal it provides to the cable plant. As noted above, the cableplant provides a gain that can change significantly over time. The gainof the cable plant and variation over time is different for differentfrequencies. Each RAD needs to have an upstream gain reference signalwhich is distinguishable at headend 40 even if the signals it generatesare combined with the signals from other RADs. More details about theoperation of the upstream gain reference signal are given below.

As noted above, a typical cellular system is comprised of a plurality ofspaced apart base stations each having a set of associated collocatedantennas. A typical cellular base station may be comprised of three ormore sectors. The sectors are subdivisions of the base station that areintimately related. Each sector transmits a different set of signalsthan the set of signals transmitted by every other sector in the basestation. Because the sector circuitry is collocated, it may be easilyshared and interconnected between the sectors. The antenna pattern of atypical three sectored base station is shown in FIG. 5. In FIG. 5coverage area 300A is represented by the finest width line. Coveragearea 300B is represented by the medium width line. Coverage area 300C isrepresented by the heaviest line. The shape of the three coverage areasshown in FIG. 5 is the shape produced by standard directional dipoleantennas. The edges of the coverage areas can be thought of as thelocation at which a remote unit receives the minimum signal levelnecessary to support communication through that sector. As a remote unitmoves into the sector, the signal strength received from the basestation as perceived by the remote unit increases. A remote unit atpoint 302 may communicate through sector 300A. A remote unit at point303 may communicate through sector 300A and sector 300B. A remote unitat point 305 communicates through sector 300B. As a remote unit movespast the edge of the sector, communication through that sector maydegrade. A remote unit operating in soft handoff mode between the basestation in FIG. 5 and an unshown neighboring base station is likely tobe located near the edge of one of the sectors.

A distributed antenna configuration is described in the above-mentionedU.S. Pat. No. 5,280,472. In the antenna system described in the '472patent, a series of antennas are strung together separated by delayelements. The series of antennas can be used to provide coverage to anelongated area or an area having a large number of attenuative objects.For example, a distributed antenna can be used to provide a signal downthe length of a sidewalk between two very tall buildings. Thedistributed antenna can easily provide coverage around corners where astandard base station coverage, such as the one shown in FIG. 5, isblocked by large buildings.

A distributed antenna system can be used to provide coverage to aconcentrated rather than elongated coverage area. For example, FIG. 6shows a set of distributed antennas 306A-306J which provide coveragearea 305A-305J respectively. A distributed antenna system is typicallyused in conjunction with a single sector of a base station. Thus each ofdistributed antennas 306A-306J transmits the same group of signals. Evenwhen delay elements are used between the antennas, each of distributedantennas 306A-306J provides the same set of signals. In addition to thegreat flexibility of the coverage area shape, distributed antennas havethe advantage of providing relatively constant signal power to theremote units within their coverage areas. Thus the remote units are ableto avoid transmitting at very high transmits levels which rapidlyconsume battery power.

In the distributed antenna arrangement of FIG. 6, as a remote unit movesbetween coverage area 305A-305J, neither the base station nor the remoteunit performs any sort of handoff. The signals which are communicatedthrough more than one of distributed antennas 306A-306J appear to boththe base station and the remote unit as multipath propagations and arediscovered, demodulated, and combined in the same manner as naturallyoccurring multipath propagations.

FIG. 7 illustrates an exemplary embodiment of a standard cellular systemshowing three single sectored base stations 362, 364, and 368. In FIG.7, each of antennas 310, 326, and 344 is the receive antenna for basestation 362, 364, or 368 respectively. Base stations 362, 364, and 368are in close proximity to one another and antennas 310, 326, and 344have overlapping coverage areas such that a single remote unit signalmay be in soft handoff with all three base stations at one time. Any oneof antennas 310, 326, and 344 may be a distributed antenna such as shownin FIG. 6. Typically base stations used diversity receive antennasmeaning that two separate antennas are used at each sector. Eachdiversity antenna is connected to its own RF receive processing thedemodulation elements can be assigned to service signals from eitherantenna. Such a diversity arrangement is not shown in FIG. 7 forclarity.

Antennas 310, 326, and 344 supply a receive signal to receiveprocessings 312, 328, and 346 respectively. Receive processings 312,328, and 346 process the RF signal and convert the signal to digitalbits. Receive processings 312, 328, and 346 may also filter the digitalbits. Receive processing 312 provides the filtered digital bits todemodulation elements 316A-316N. Receive processing 328 provides thefiltered digital bits to demodulation elements 332A-332N. Likewise,receive processing 346 provides the filtered digital bits todemodulation elements 350A-350N.

Demodulation elements 316A-316N are controlled by controller 318 throughinterconnection 320. Controller 318 assigns demodulation elements316A-316N to one of the instances of information signal from the sameremote unit as perceived by base station 362. The distinct instances ofthe signal may be created due to the multipath characteristics of theenvironment. Demodulation elements 316A-316N produce data bits 322A-322Nthat are combined in symbol combiner 324. The output of symbol combiner324 may be aggregate soft decision data suitable for Viterbi decoding.The combined data is decoded by decoder 314 and output as Message 1 andpassed to cellular or personal communications system controller 370.

A power adjustment command from base station 362 for the remote unit iscreated by controller 318 from the combined signal strength of all thesignals demodulated by demodulation elements 316A-316N. Controller 318can pass the power control information to the transmit circuitry (notshown) of base station 362 to be relayed to the remote unit.

Demodulation elements 332A-332N are controlled by controller 334 throughinterconnection 336. Controller 334 assigns demodulation elements332A-332N to one of the instances of information signals from the sameremote unit. Demodulation elements 332A-332N produce data bits 338A-338Nthat are combined in symbol combiner 340. The output of symbol combiner340 may be aggregate soft decision data suitable for Viterbi decoding.The combined data is decoded by decoder 342 and output as Message 2 andpassed to cellular or personal communications system controller 370.

A power adjustment command for the remote unit is created by controller334 from the combined signal strength of all the signals demodulated bydemodulation elements 332A-332N. Controller 334 can pass the powercontrol information to the transmit circuitry (not shown) of basestation 364 to be relayed to the remote unit.

Demodulation elements 350A-350N are controlled by controller 352 throughinterconnection 354. Controller 352 assigns demodulation elements350A-350N to one of the instances of information signals from the sameremote unit as perceived by base station 368. Demodulation elements350A-350N produce data bits 356A-356N that are combined in symbolcombiner 358. The output of symbol combiner may be aggregate softdecision data suitable for Viterbi decoding. The combined data isdecoded by decoder 360 and the output as Message 3 and passed tocellular or personal communications system controller 370.

A power adjustment command for the remote unit is created by controller352 from the estimated signal strengths of all the signals demodulatedby demodulation elements 350A-350N. Controller 352 can pass the powercontrol information to the transmit circuitry (not shown) of basestation 368 to be relayed to the remote unit.

For each remote unit operating in soft handoff in the system, cellularor personal communication system controller 370 receives decoded datafrom at least two base stations. For example, in FIG. 7 cellular orpersonal communications system controller 370 receives decoded data inthe form of Messages 1, 2, and 3 from the common remote unit from basestations 362, 364, and 368 respectively. The decoded data cannot becombined to yield the great advantage that is achieved by combining thedata prior to decoding. Therefore typically cellular or personalcommunication system controller 370 does not to combine the decoded datafrom each base station and instead selects one of the three decoded dataMessages 1, 2, or 3 having the highest signal quality index and discardsthe other two. In FIG. 7 selector 372 performs the selection process ona frame by frame basis and provides the result to a vocoder or otherdata processing unit. More information about the selection process canbe found in copending U.S. patent application Ser. No. 08/519,670entitled "COMMUNICATION SYSTEM USING REPEATED DATA SELECTION" assignedto the assignee of the present invention.

The reason why the combined but undecoded data output from symbolcombiners 324, 340, and 358 is not sent respectively from base stations362, 364, and 368 to system controller 370 is that the demodulationprocess produces data at a very high rate. A large block of data is usedin the decoding process to produce the decoded symbol. The ratio of theamount of data necessary to decode a data symbol and the amount of datato specify a decoded symbol and quality index can be as high as 1000to 1. In addition to the complexity, the inherent delay of transportingsuch large amounts of data is prohibitive unless a very high speed linkis used. Thus the interconnection system between the hundreds of basestations in the system (most of which are not shown in FIG. 7) andsystem controller 370 is greatly simplified by sending only the decodeddata and quality indications instead of the undecoded data suitable forcombination.

Aside from the complexity of transmitting the large amount of dataassociated with combined but undecoded data, the cost is alsoprohibitive. Typically the base stations of a system are remotelylocated from the system controller. The path from the base stations tothe system control typically comprises a leased line such as a T1interface line. The cost of these lines is largely determined by theamount of data that they carry. Thus increasing the amount of data thatis transmitted from the base stations to the system controller can becost prohibitive as well as technically difficult.

In a less than optimal system the selection method of soft handoffdescribed with respect to FIG. 7 could be directly applied to asectorized base station by treating each sector of a common base stationas a separate, independent base station. Each sector of the base stationcould combine and decode multipath signals from a common remote unit.The decoded data could be sent directly to the cellular or personalcommunication system controller by each sector of the base station or itcould be compared and selected at the base station and the result sentto the cellular or personal communication system controller. But a muchmore advantageous method of handling handoff between sectors of a commonbase station is to use softer handoff as described in theabove-mentioned U.S. patent application Ser. No. 08/144,903. Circuitryfor providing softer handoff is described in conjunction with FIG. 8.

In FIG. 8, each of antennas 222A-222C is the receive antenna for onesector and each of antennas 230A-230C is the transmit antenna for onesector. Antenna 222A and antenna 230A correspond to a common coveragearea and can ideally have the same antenna pattern. Likewise antennas222B and 230B, and antennas 222C and 230C correspond to common coverageareas respectfully. FIG. 8 represents a typical base station in thatantennas 222A-222C have overlapping coverage areas such that a singleremote unit signal may be present at more than one antenna at a time.Antennas 222A-222C may provide antenna patterns as shown in FIG. 5 orone or more of antennas 222A-222C may be distributed antennas.

Referring again to FIG. 8, antennas 222A, 222B, and 222C supply thereceived signal to receive processings 224A, 224B, and 224Crespectively. Receive processings 224A, 224B, and 224C process the RFsignal and convert the signal to digital bits. Receive processings 224A,224B, and 224C may filter the digital bits and provide the resultingdigital bits to interface port 226. Interface port 226 may connect anyof the three incoming signal paths to any of the demodulation elements204A-204N under the control of controller 200 through interconnection212.

Demodulation elements 204A-204N are controlled by controller 200 throughinterconnection 212. Controller 200 assigns demodulation elements204A-204N to one of the instances of information signals from a singleremote unit from any one of the sectors. Demodulation elements 204A-204Nproduce data bits 220A-220N each representing an estimate of the datafrom the single remote unit. Data bits 220A-220N are combined in symbolcombiner 208 to produce a single estimate of the data from the remoteunit. The output of symbol combiner 208 may be aggregate soft decisiondata suitable for Viterbi decoding. The combined symbols are passed todecoder 228.

Demodulation elements 204A-204N also provide several output controlsignals to controller 200 through interconnection 212. The informationpassed to controller 200 includes an estimate of the signal strength ofthe signal assigned to a particular demodulation element. Each one ofdemodulation elements 204A-204N measures a signal strength estimation ofthe signal that it is demodulating and provides the estimation tocontroller 200.

Notice that symbol combiner 208 can combine signals from just one sectorto produce an output or it can combine symbols from multiple sectors asselected by the interface port 226. A single power control command iscreated by controller 200 from the estimated signal strengths from allof the sectors through which the signal is received. Controller 200 canpass the power control information to the transmit circuitry of eachsector of the base station. Thus each sector in the base stationtransmits the same power control information to a single remote unit.

When symbol combiner 208 is combining signals from a remote unit that iscommunicating through more than one sector, the remote unit is in softerhandoff. The base station may send the output of decoder 228 to acellular or personal communication system controller. At the cellular orpersonal communication system controller, signals from this base stationand from other base stations corresponding to the remote unit may beused to produce a single output using the selection process describedabove.

The transmit process shown in FIG. 8 receives a message for a remoteunit from the end user through the cellular or personal communicationsystem controller. The message can be sent on one or more of antennas230A-230C. Interface port 236 connects the message for the remote unitto one of more of modulation elements 234A-234C as set by controller200. Modulation elements 234A-234C modulate the message for the remoteunit with the appropriate PN code. The modulated data from modulationelements 234A-234C is passed to transmit processing 232A-232Crespectively. Transmits processings 232A-232C convert the message to anRF frequency and transmit the signal at an appropriate signal levelthrough antennas 230A-230C respectively. Notice that interface port 236and interface port 226 operate independently in that receiving a signalfrom a particular remote unit through one of antennas 222A-222C does notnecessarily mean that the corresponding transmit antenna 230A-230C istransmitting a signal to the particular remote unit. Also note that thepower control command sent through each antenna is the same, thus sectordiversity from a common base station is not critical for the optimalpower control performance. These advantages are further exploited to theadvantage of the system in the above-mentioned U.S. patent applicationSer. Nos. 08/144,901 and 08/316,155 through a process referred to astransmit gating.

Note the increased flexibility of the base station resources. ComparingFIG. 7 to FIG. 8, the flexibility is apparent. In the three basestations represented in FIG. 7, suppose that base station 362 is heavilyloaded with signals such that the number of incoming signals is greaterthan the number of demodulation elements can handle. The fact that basestation 364 is lightly loaded and has unused demodulation elements doesnot aid base station 362. In FIG. 8, however, each demodulation elementmay be assigned to any one of a plurality of sectors thus allowingallocation of resources to the most heavily loaded sector.

In the present invention there is only one centralized base station atheadend 40. (See FIG. 2.) Thus all the demodulation elements in thesystem may be considered to be intimately related in the same manner asthe sectors of a standard system. Signals from any RAD may be combinedbefore decoding with a signal from any other RAD thus providing animproved system performance. In the most ideal configuration the processof selection is eliminated and softer handoff may be provided over theentire coverage area of the system. Note that in the interest ofsimplified architecture, it may be advantageous to limit theinterconnectivity between the demodulation elements and use selection tocombine some signals some of the time.

In addition to the great benefits of providing softer handoff throughoutthe system, the extreme flexibility of such a system makes it simple tobegin initial deployment of a system and to reconfigure the system toadapt to changes in the system. The flexibility comes from the fact thatin a system as described herein, each RAD can operate either as a nodeof a distributed antenna or an independent sector and the role of theRAD may be changed simply, quickly, and remotely by headend 40.

FIG. 9A is an exemplary spectral distribution on the downstream cableplant link. Because traditional television channels on the cable plantare allotted 6 MHz of bandwidth, the forward link signaling uses 6 MHzfrequency blocks in the preferred embodiment. Also, a typical basestation is comprised of three sectors. Thus to conform with thetraditional cellular equipment, the frequency is allotted with referenceto three related sectors. Obviously many other frequency distributionsand resource allocations could fit easily within the concepts of thepresent invention. If FIG. 9A, the CDMA waveform for three sectors isshown. In the preferred embodiment the CDMA waveform is approximately1.25 MHz wide for each sector. Also shown in FIG. 9A is the RADreference signal which is monitored by RAD transmitting any one of thethree sectors shown. The sharp SAW filter in the RADs can reject theother CDMA waveforms and the RAD reference signal at the RAD to asufficient level such that only the desired signal is transmitted overthe wireless link to the remote units.

FIG. 9B is an exemplary spectral distribution on the upstream cableplant link. The reverse link signaling is less constrained bytraditional upstream spectrum frequency allocation. In the allocationshown in FIG. 9B, it is assumed that at least some of the RADs areequipped with alpha and beta diversity antennas such as the exemplaryRAD shown in FIG. 4. Therefore a larger allocation of upstream bandwidthis needed to service the three sectors. In the exemplary configurationshown in FIG. 9B, 13 MHz is allocated as shown with a portion of thespectrum allocated for the RAD unique upstream gain reference signal.

As apparent from FIGS. 9A and 9B, the sector signals are frequencymultiplexed onto the cable. A RAD can be commanded via the RAD referencesignal to tune its PLLs such that the sector 1 frequency is transmittedfrom the RAD and such that the RAD supplies its received signal to thesector one-alpha and sector one-beta frequencies. A second RAD having acontiguous coverage area can be commanded to transmit and receive sector1 as well. Thus the second RAD behaves as if it were another antennawith the first RAD in a distributed antenna configuration. This is truewhether or not the first and second RADs are connected to the same ordifferent fiber nodes (for example fiber nodes 20A-20I of FIG. 2). Inthis case a remote unit passing from the coverage area of the first RADto the coverage area of the second RAD does not perform a handoff atall. Both the remote unit and base station processing perceive thechange in coverage areas as simply the creation of a new multipathpropagation.

Alternatively the second RAD can be commanded via the RAD referencesignal to tune its PLLs such that the sector 2 frequency is transmittedfrom the RAD and such that the RAD supplies its received signal to thesector two-alpha and sector two-beta frequencies. In this case, as aremote unit moves from the coverage area of the first RAD to thecoverage area of the second RAD, the remote unit performs a handoff asdescribed above. Depending on the base station configuration, the basestation performs a soft or softer handoff of the remote unit. Typicallythe soft and softer handoff are perceived the same from the remote unitperspective.

FIG. 10 illustrates an exemplary block diagram of a base station inaccordance with the present invention. In particular, FIG. 10 shows basestation 44 of FIG. 2 in detail. Base station 44 receives input fromoptical to electrical signal converters 18A-18I. In the most generalcase, each of optical to electrical signal converters 18A-18I maycontain signals for any one of K different sectors supported by basestation 44. Dual bank of downconverters 410A-410N is coupled to opticalto electrical signal converters 18A-18I via interconnection 414. Thedual nature of the downconverters 410A-410N reflects the fact that thefiber strands may contain both an alpha and a beta diversity reception.If there are some RADs that do not provide diversity reception, some ofthe downconverters need not be dual in nature. In the most general case,interconnection 414 is capable of connecting any one of optical toelectrical signal converters 18A-18I to any one of dual bank ofdownconverters 410A-410N and may be capable of combining signals fromtwo or more of optical to electrical signal converters 18A-18I.

With reference to FIG. 9B, it is easy to see that to downconvert eachsignal from each incoming sector to a common IF frequency there is not aone to one correspondence between downconverters and optical toelectrical signal converters. For example if optical to electricalsignal converter 18A provides only the signals corresponding to thethree sectors shown in FIG. 9B, there must be six differentdownconverters--one corresponding to each of sectors 1-alpha, 1-beta,2-alpha, 2-beta, 3-alpha, and 3-beta--receiving a signal from optical toelectrical signal converter 18A. In the preferred embodiment, if opticalto electrical signal converter 18A and optical to electrical signalconverter 18B each carries signals corresponding to sector 1-alpha atthe same frequency, those signals could be combined in interconnection414 before downconversion.

In the most general case, the fact that a given sector of the Kdifferent sectors supported by base station 44 is carried at a firstfrequency on a first one of the fibers within the cable plant does notnecessarily mean that other fibers carry the same sector at the firstfrequency. Thus even in a system with as few as three sectors and withthe ability to combine signals at RF within interconnection 414, morethan a two-to-one ratio between the number of supported sectors (K) tothe number of downconverters in the dual bank (N) are required. Forexample, if optical to electrical signal converter 18A carries the setof three sectors shown in FIG. 9B centered about 12 MHz and optical toelectrical signal converter 18B carries the set of three sectors shownin FIG. 9B centered about 25 MHz, then 12 different downconverters arenecessary to service the three sectors.

Dual bank of downconverters 410A-410N provide down conversation andfiltering of the incoming signals. In the preferred embodiment, thesignal output from each of dual bank of downconverters 410A-410N is acommon IF frequency.

In parallel with dual bank of downconverters 410A-410N are upstream gainreference signal processors 412A-412M. Interconnection 414 also providesinterconnection between the upstream gain reference signal (as exemplaryshown in FIG. 9B) from optical to electrical signal converters 18A-18Ito upstream gain reference signal processors 412A-412M. The upstreamgain reference signal from each RAD must still be separately analyzed atbase station 44 and thus the number of upstream gain reference signalprocessors (M) is not set by the number of dual downconverters (N). Inthe preferred embodiment, the upstream gain reference signal need onlybe monitored at intervals rather than continually. For example eachupstream gain reference signal processors 412A-412M could be assigned tomonitor up to 12 different upstream gain reference signals at one timeby sequentially measuring the power level in each. In such a case, theactual number of upstream gain reference signal processors (M) can belowered.

Upstream gain reference signal processors 412A-412M measure theamplitude of the upstream gain reference signal of each RAD. Themeasurement of the upstream gain reference signal provides an estimateof the relative amplitudes of the upstream signals. The result of themeasurements is reported to cable plant communication controller 430over interconnection 408. A message is sent back via the RAD referencesignal to the corresponding RAD commanding the RAD to increase ordecrease the level of the upstream signals it provides. Thus therelative signal levels output from each RAD is controlled such that thesignals may be properly combined within the cable plant or within basestation 44. Upstream gain reference signal processors 412A-412M may alsoprovide other functions such as monitoring for messages from the RADs orfault management.

Interconnection 408 performs interconnection between dual bank ofdownconverters 410A-410N to dual bank of summers 407A-407K. Dual bank ofsummers 407A-407K sum together the output from each of downconverters410A-410N which correspond to the same sector.

In addition to the fact that the upstream power from each RAD needs tobe controlled relative to the others so that effective combining can beaccomplished, headend 40 must also regulate the absolute level of theupstream signal. As noted above, one of the unique problems of using thecable plant to provide distribution of personal communication signals isthe presence of ingress signals. The CDMA system of the preferredembodiment is inherently tolerant of the adverse effects of evenrelatively large jammers injected in the wireless environment andingress signals injected in the cable plant due to both the broadbandnature of the information signal and the reverse link power controlmechanisms employed in the system. The reverse link power controlmechanism controls the reverse link signal to a very limited dynamicrange as received by the RADs. Each remote communication unit adjustsits transmit power so that the RAD receives the remote unit signal atthe same level regardless of the distance between the remote unit andthe RAD. Because the reverse link power has a relatively low dynamicrange, the upstream cable plant signal can have a consistently highpower level operating point within the cable plant thus providingconsistent advantages over lower power level ingress signals.

However, it is also important that the operating point of the uplinkremain low enough so as to not overload the electrical to opticalconverters and other devices in the path. The operating point of thereverse link upstream signals must also be low enough so as to not causedegradation to the other upstream cable plant signals such as"pay-per-view" indication signaling coming from the cable T.V.subscribers. Thus headend 40 must also address the absolute level of theupstream signals on the cable plant.

Using the architecture shown in FIG. 10, numerous methods exists bywhich the absolute level can be controlled. Remember that the upstreamgain reference signal reaches headend 40 at the same level regardless ofthe actual signal level received from the corresponding RAD. Thereforeanother method must be used by which to determine the total power. Onemethod is have each active one of dual bank of down converters 410A-410Nreport to cable plant communication controller 430 the absolute level ofthe signals it is receiving. In response thereto, cable plantcommunication controller 430 can command each RAD to increase ordecrease the signal level at which it is supplying the upstream signal.

The output of each of dual bank of summers 407A-407K is provided to acorresponding one of dual bank of automatic gain control (AGC) units406A-406K. Each of dual bank of automatic gain control 406A-406K provideIF signal processing such as filtering. In the preferred embodiment dualbank of down converters 410A-410N output analog signals which arecombined by analog dual bank of summers 407A-407K. The combined analogsignal is converted to a digital signal within dual bank of automaticgain control units 406A-406K. In order for the analog to digitalconverters to work properly, the amplitude of the analog signal inputinto the analog to digital converters must be carefully controlled. Theautomatic gain control function of the dual bank of automatic gaincontrol units 406A-406K is the process of setting the combined analogsignal to the proper level for conversion and does not effect the cableplant power control loops. Alternatively, the A/D converters can belocated within modem 400.

Modem bank 400 is connected to dual bank of automatic gain control units406A-406K through interconnection 404. Modem bank 400 houses a pluralityof digital shelves 402. Each digital shelf is comprised of a bank ofchannel element modems. The channel element modems perform the functionsthe demodulation elements (such as demodulation elements 204A-204N ofFIG. 8). In the most general case, each demodulation element in modembank 400 may be assigned to any one of the sector signals coming fromany one of dual bank of automatic gain control units 406A-406K.

FIG. 12 shows a partial block diagram of one of the channel elementmodem in digital shelves 402 using the same numerology for like elementsas the elements of FIG. 8. The channel element modem shown in FIG. 12 isused to process signals corresponding to one remote unit. In the mostideal preferred embodiment, each one of demodulation elements 204A-204Nmay be assigned to demodulate one multipath signal from any one of dualbank of automatic gain control units 406A-406K through interconnection404. Thus more than one of demodulation elements 204A-204N may beassigned to the same one of dual bank of automatic gain control units406A-406K if more than one usable multipath signal is being receivedfrom the same one of dual bank of automatic gain control units406A-406K. Also one of demodulation elements 204A-204N may be assignedto a different one of dual bank of automatic gain control 406A-406K ifthe remote unit signal is being received on two distinct unmerged pathsthrough the cable plant. Note that the output of each of demodulationelements 204A-204N is combined in symbol combiner 208 weighted accordingto signal quality independent of which of dual bank of automatic gaincontrol units 406A-406K is supplying the signal and there is no use ofthe process of selection thus providing soft handoff over the entirecoverage area.

FIG. 12 also shows the modulation portion of one of the channel elementmodems within one of digital shelves 402. In the preferred embodiment,the forward link traffic channel signal is modulated by the pilotsequence before transmission. If the forward link signal created is tobe supplied from two RAD units operating in association with differentpilot signal offsets, the forward link signal needs to be created by twodifferent modulation elements. Modem bank controller 237 performsanalogous control functions through bus 237 to controller 200 of FIG. 8.

Interconnection 414, interconnection 404, interconnection 426, andinterconnection 408 ideally can connect any one of the inputs to any oneof the outputs thereto. Especially in very large systems, actualpractical implementations may limit the interconnectivity for monetary,spatial, or other practical reasons. For example, it may be advantageousto limit the interconnectivity such that a first set of optical toelectrical signal converters can be coupled to a first set ofdownconverters but cannot be coupled to a second set of downconverters.The connection configuration of interconnection 414, interconnection408, interconnection 426, and interconnection 404 are dynamicallycontrollable by cable plant communication controller 430. (For clarity,some connections are not shown in FIG. 10.)

The transmit signals are created in digital shelves 402. For each activesector, a complete set of signals comprising the pilot channel, syncchannel, paging channels, and all traffic (i.e. mobile specificcommunication) channels are output from digital shelves 402 and inputinto interconnection 404. Each sector signal output from modem bank 400is upconverted by at least one of upconverters 422A-422P. If the sectorsignal is to be transmitted on multiple strands at differentfrequencies, the sector signal is provided to more than one ofupconverters 422A-422P.

For each sector signal, a digital indication of the desired transmitsignal level is sent to one or more of RAD reference generators420A-420L. Every strand carrying a sector signal must also carry acorresponding RAD reference signal which provides the downstream powercontrol information, upstream power control information, and any othercontrol information corresponding to RADs on the strand monitoring oneof the sector signals.

If in an alternative embodiment a digital indication of the desiredtransmit signal level is not generated by digital shelves 402, a powermonitoring circuit could be added in front of upconverters 422A-422Pwhich would measure the power in the incoming sector signals. Themeasured power level would be directly or indirectly reported to theappropriate one of RAD reference generators 420A-420L which would actupon the measured value in the same way as it acts in the preferredembodiment upon the digital indication of the desired transmit signallevel.

If a single strand is providing three different sector signals to RADson the same strand as shown in FIG. 9A, three different digitalindications of the desired transmit signal level are sent to a singleone of RAD reference generators 420A-420L. For each RAD monitoring thesector signal on this strand, upstream power control information mustalso be provided. This information is provided from cable plantcommunication controller 430 as derived from upstream gain referencesignal processors 412A-412M.

Interconnection 426 must be capable of coupling output from a pluralityof upconverters 422A-422P to one or more of electrical to optical signalconverters 16A-16I. If multiple strands are transmitting the same sectorinformation carried in the cable plant at the same frequency, the sameupconverter can drive multiple electrical to optical signal converters16A-16I. If the multiple sectors are transmitted on the same strand asshown in FIG. 9A, more than one of upconverters 422A-422P is coupled tothe same one of electrical to optical signal converters 16A-16I.Interconnection 426 also couples the corresponding RAD reference signalfrom one of RAD reference generators 420A-420L to each of electrical tooptical signal converters 16A-16I. If the RAD reference signal hassufficient information bandwidth to provide power control and othercontrol information, the same RAD reference signal may be coupled to aplurality of electrical to optical signal converters 16A-16I.Alternatively a different RAD reference signal may be generated for eachstrand even if the strands are carrying the same sector signals. In sucha case, the RAD reference signal carries only control informationcorresponding to those RADs on the strand.

Like the upstream link, the absolute level of the downstream link mustalso be controlled. Typical cable downstream T.V. signals operate atabout 112 dB/Hz (decibels/Hertz.) In the preferred embodiment, the CDMAsignal levels could be reduced from that level by approximately 10 dB toensure that the CATV performance is not impacted by the CDMA signaling.

Interconnection 414 also provides connection from optical to electricalsignal converters 18A-18I to ingress processor 416. The functions ofingress processor 416 are described in detail below.

In typical macrocellular system, the base stations do not interfacedirectly with the PSTN. Typically a centralized system controllerprovides control over a set of base stations. For example, FIG. 7 showssystem controller 370 providing the selection process for base stations362, 364, and 368. In the preferred embodiment the process of selectionmay be eliminated but there are other functions of the centralizedcontroller which may now be delegated to headend 40. For example, a CDMAsystem designed in accordance with the "Mobile Station-Base StationCompatibility Standard for Dual-Mode Wideband Spread Spectrum CellularSystem," TIA/EIA/IS-95, generally referred to simply as IS-95 providesfor voice data which is vocoded into frames. System controller 370provides the conversion between the pulse code modulation (PCM)signaling used over the PSTN and the vocoded frames used in the CDMAsystem.

In the preferred embodiment, the system provides for both voice and dataservice operation from the remote units. The headend may also need toprovide various data service functions typically performed by a systemcontroller in a macrocellular system. The headend may also need toperform the billing functions and other call processing functionsusually handled by the system controller. The headend may also comprisea switch for switching calls between the CATV system and the PSTN.

A variety of architectures and function allocations are consistent withthe present invention. For example, the traditional functions of thesystem controller may remain delegated to a separate system controllerand the headend may be treated as one or several base stations of alarger system.

As noted above the RAD reference signal is used in three ways by theRADs. First, the RAD reference signal is to convey digital informationto the RAD. Second, it is used as a frequency reference within the RAD.Third, the RAD reference signal is used as a reference by which thecable plant gain is measured. One method which allows the RAD referencesignal to perform all three functions is if the RAD reference signal isan amplitude modulated (AM) signal.

In the preferred embodiment, each RAD in a system is assigned its ownunique address. In reality, it is only necessary that each RAD assignedto monitor a common RAD reference signal has a unique address andtherefore the addresses could be repeated throughout the system. In themost flexible design, even the RAD addresses are remotely programmablefrom by headend 40 but the address could also be fixed in hardware. TheRAD signaling format can use a standard signaling format in which eachRAD monitors the RAD reference signal for its own address. When theaddress transmitted on the RAD reference signal corresponds to the RADaddress or an universal address, the RAD decodes the following messageand acts upon it if necessary. If the address does not correspond to theRAD address or an universal address, the RAD simply ignores thefollowing message but continues to monitor the RAD reference signal. Theexpected signal rate required of the RAD reference signal is only about300 bits per second (bps) but a standard modem rate of 9.6 kilobps(kbps) or 19.2 kbps could easily be used.

The second use of the RAD reference signal is as a frequency referencefor the PLL in the RAD. The RAD reference signal is also used as afrequency reference for the RAD clock to synchronize the transfer ofdata. As an AM modulated signal, the frequency of the signal remainsconstant over time and the signal can be used almost directly as areference. In addition, to avoid amplitude and phase modulationdistortion, the modulation used should be fairly fast and have no DCcontent. A modulation techniques, such as Split-Phase or Manchestermodulation, which provide an "M" shaped spectral densities can be usedso that the distortion is not located in close to the carrier.

The third use of the RAD reference signal is to approximate the gain ofthe cable plant between headend 40 and each RAD. The amplitude modulatedsignal can be used as an amplitude reference if the modulation scheme iscarefully designed. For example, the AM modulation index should be keptrelatively low. The digital data transmitted should contain an equalnumber of logical 1's and 0's over relative short intervals. It is alsonecessary that the RAD average the power of the RAD reference signalover some period of time.

As noted in the background section above, the power of the aggregateforward link CDMA signal carried on the downstream cable plant is afunction of the number and relative power of the signals which arecombined to create the aggregate forward link signal. Also for thereasons noted above, it is important that the relative power transmittedby each RAD is properly controlled so that the handoff boundaries remainproperly aligned between the RADs. A method and apparatus for creating again signal indicative of an appropriate aggregate signal strength isdetailed in U.S. patent application Ser. No. 08/525,899, filed Sep. 8,1995, entitled "APPARATUS AND METHOD FOR CONTROLLING TRANSMISSION POWERIN A CELLULAR COMMUNICATIONS SYSTEM" assigned to the assignee of thepresent invention.

Each sector in the system has an independent aggregate signal strengthbased on the number and relative signal strength of each signal that ittransmits. Each modulation element in digital shelves 402 generating asignal outputs a digital signal which is added to the other indicationsoutput from modulation elements producing signal for the same sector. Inthis way an aggregate transmit level indication, which may be created inaccordance with the just mentioned U.S. patent application Ser. No.08/525,899, indicates the aggregate signal strength of each sectorsignal modem bank 400 creates.

At the same time, the RAD reference signal is transmitted at a fixedlevel by headend 40 at all times regardless of the desired output power.The RAD reference signal can be used as a coarse estimate of the cableplant gain. Referring again to FIG. 3, as the RAD is radiating power,the output power is detected by power detector 90 and reported back toRAD microprocessor 88. RAD microprocessor 88 compares the measuredtransmit power level with the level indicted in digital form as receivedin the digital information on the RAD reference signal. From thecomparison a resultant difference signal is produced representing theamount by which the output power should be lowered or raised. This powercontrol loop is executed with a first time constant consistent with thespeed at which the power control commands are received from headend 40over the RAD reference signal. Note that every RAD radiating the signalcorresponding to this sector receives the same power indication in thedigital information on the RAD reference signal. As it is the goal ofthe power control loops to hold the output power within +/-1 dB of thedesired output level, the first loop may need to operate quite slowly inorder to provide the precise output power desired.

At the same time RAD microprocessor 88 is executing the first powercontrol loop, it is also monitoring the absolute level of the RADreference signal. Note that the gain between each RAD and headend 40 isdifferent and some what independent in that each RAD has a distinct pathto headend 40 different than every other RAD. Without the second loop,if conditions changed in the path between headend 40 and the RAD, theoutput power of the RAD would also change until the first power controlloop could bring the level back to the desired level.

However, the RADs use a second power control loop to compensate forchanges in the cable plant gain. RAD reference signal processor 84monitors the absolute level of the RAD reference signal and compares itto a fixed reference. The result of the second comparison is added tothe result of the comparison of the first power control loop. The summedsignal is output to gain control 72 which sets the output power of theRAD. Thus when the gain of the cable plant changes, the gain of the RADchanges accordingly.

In other embodiments, only one of the previous methods of power controlmay be implemented. Such modifications are within the scope of thepresent invention.

From the previous description of the forward link power control, it isevident that the more closely the RAD reference signal represents theactual gain or change in gain of the cable plant the more precisely theupstream power control works. In the cable plant, the gain variationsover time can have a significant frequency dependence. Therefore thelarger the frequency offset between the sector signal and thecorresponding RAD reference signal, the lower the correlation of thegain variations of the sector signal to the gain variations of the RADreference signal. For example, referring again to FIG. 9A, the amplitudeof the RAD reference signal shown may provide a good indication of theamplitude of sector 3 while providing a less accurate estimate of theamplitude of sector 1.

Another factor which is evident from an examination of FIG. 9A is thatthe RAD reference signal itself occupies bandwidth which could be usedfor other purposes such as another sector signal or a T.V. signal.

One method to more closely couple the amplitude characteristics of theRAD reference signal and the sector signal is to transmit the RADreference signal at a frequency within the 1.25 MHz CDMA sector signalbandwidth. FIG. 11 shows a scenario in which the RAD reference signal isplaced in the center of the CDMA sector signal. The presence of the RADreference signal within the CDMA waveform does not greatly effect theperformance of the system. The PN spreading sequence used in the remoteunits to demodulate the sector signal inherently provides a significantcoding gain to the CDMA signal relative to the RAD reference signal"jammer" energy.

Placing the RAD reference signal in the center of the CDMA sector signalmay have additional benefits over placing the RAD reference signalelsewhere in the sector signal. In the remote units, the CDMA waveformis converted to base band such that the center frequency of the RFsignal maps to a D.C. value at base band. The D.C. value of the analogCDMA waveform is blocked by analog circuitry before it is digitallyconverted thus providing an additional rejection mechanism of a signalat that frequency.

A similar technique could be used for the upstream gain referencesignal. However this solution is less elegant on the upstream linkbecause of the number of upstream gain reference signals for each sectormay be quite large thus proportionally increasing the amount ofinterference.

As noted above, the cable plant radio frequency (R.F.) environment isespecially hostile. The cable plant is highly susceptible to ingresssignals that are likely to develop and change over time. Also as notedabove, the CDMA waveform properties are inherently protected from narrowband interference. Therefore if a narrow band jammer develops within thespectrum of the upstream sector signals, the system performance may beslightly degraded. However no real mechanism exists within the CDMAcircuitry to detect the cause of the degradation.

Ingress processor 416 of FIG. 10 performs this function. Ingressprocessor 416 surveys the entire usable spectrum in narrow bandincrements to create a data base of the location of jammers. Forexample, ingress processor 416 samples a 125 kHz piece of spectrum overa 10 millisecond (msec) interval. If the energy observed in thatbandwidth exceeds the energy attributable to the CDMA waveform (which isrelatively small due to the broadband nature of the CDMA signal and thenarrow band nature of the measurement), ingress processor 416 registersa "jammer" at that frequency. Of the sum of the jammer energy within oneof the sector signals exceeds a threshold, the sector signal may bemoved to another frequency. The new frequency may be chosen in view offthe data base of jammers stored within ingress processor 416 such thatthe cleanest possible spectrum is used.

The transition to the new frequency may be easily accomplished withoutinterruption of the communication between the RAD and the headend. Theset of RADs providing signals at the infected bandwidth are notified viathe RAD reference signal to provide the signal at a new frequency. Forexample in FIG. 4, either PLL 112 or PLL 138 or both could bereprogrammed to a new frequency. At headend 40 one of dual bank of downconverters 410A-410N is commanded to begin processing the signalsarriving at the new frequency. Note that this entire operation can occurautomatically without any human intervention.

The system just described has a great number of advantages in theflexibility it provides When the system is first deployed, the number ofusers is relatively low. At such an initial deployment, headend 40 maycomprise a single sector of resources meaning that every RAD in thesystem provides the same set of signals. Remote units can travel throughthe entire system without a handoff being performed.

As the number of remote users increases, additional resources to providean additional sector can be added at the base station. For example, anew sector requires additional digital shelves and may requireadditional upconverters and downconverters. When the new base stationcircuitry is in place, a number of the RADs can be programmed by theheadend to operate as the new sector signal. As the number of remoteunits increases further, more resources are added at the base stationand more of the RADs are remotely programmed. Note that the addition ofthe new sectors does not require any changes to the physical RADs. Theprogramming which must take place is accomplished by the base stationremotely. Thus in addition to the low start up cost required toimplement a system, the system can be expanded slowly, easily, andinexpensively.

The ease at which the RADs can be re-programmed to operate as a newsector, may also be taken advantage of when the requirements of thesystem change. For example, assume that a normally urban area is coveredby a series of 5 RADs all of which transmit the same set of signals asdistributed antennas of a common sector. In the small area covered bythe series of 5 RADs the amount of remote units attempting to use thesystem suddenly triples due to an unexpected event such as an automobileaccident which backs up traffic. The base station is cognizant of thefact that the number of attempts to access the system through thecorresponding sector has dramatically increased. The base station canreprogram one or more of the 5 RADs to begin to operate as anothersector thus increasing the total number of simultaneous telephone callswhich can be serviced in the area. In the most extreme case, each of thefive RADs can become a sector unto itself. The base station can do sonearly instantly without the aid of human intervention.

This flexibility feature, which is quite unique to the present inventionas compared to conventional macrocellular systems, has boundlesspossibilities. Another example of a use would be for areas of sporadicutilization. For example, a sports stadium may be crowed for severalhours several times a week but may be nearly deserted the remaininghours. In conventional fixed systems, if sufficient resources wereprovided to service all of the remote units during the sporting events,the resources would remain idle during a majority of the time. Howeverin the present invention, the resources can be allocated to the stadiumareas when needed and used throughout the rest of the system when theyare not being used at the stadium thus decreasing the cost of the systemand increasing the effective capacity. The allocation can bepreprogrammed at the headend in view of the known and expected events orthe same automatic response to the increase in traffic used in the caseof the automobile scenario above can be used.

There are various modifications within the scope of the presentinvention. For example as noted above, IF processor 70 in FIG. 3 maycomprise a fixed delay element to provide the delay necessary to creatediversity signals which can be separately demodulated at the remoteunits. In an alternative embodiment, more than one version of a sectorsignal could be transmitted over the downstream link of the cable plant.The versions could be delayed at the headend processor or elsewhere inthe system and the various RADs acting as distributed elements of acommon distributed antenna could transmit the different versions havingthe different delays rather than providing their own delay.

Another way to provide greater signal carrying capacity on the upstreamlink is to provide a mechanism of frequency conversion in fiber nodes20A-20I. On the link from the RADs to the fiber nodes, the upstreambandwidth of the system is limited to the 5-40 MHz range and thedownstream bandwidth of the system is limited to the 54 MHz to 700 MHzrange. The optical network actually capable of carrying signals over amuch greater bandwidth such as 200 MHz. Each fiber node could use acommon set of frequencies to carry the upstream signal from the RADs tothe fiber node. The fiber nodes could frequency multiplex the upstreamsignal to a set of frequencies above the operating frequency of thedownstream link to carry the signal between over the optical network tooptical to electrical signal converters 18A-18I. Optical to electricalsignal converters 18A-18I could either downconverter the signals beforeproviding them to base station 44 or dual bank of down converters410A-410N could provide the necessary down conversion.

In the first generation implementation of the present invention, it maybe most financially advantageous to build the circuitry at headend 40from the existing circuitry used in macrocellular systems. A typicalfixed location macrocellular base station is comprised of threedifferent sectors. Softer handoff/combination is executed to handoffbetween the three sectors of a common base station and the softhandoff/selection is used to handoff between any one of the sectors anda sector of another base station. To use existing equipment, thearchitecture of the headend could be implemented in triple sector sets.Handoff between the sectors of a triple sector set would be softer whilehandoff between sectors of uncoupled sector triples would be softhandoffs. The most advantageous implementation of such a system wouldprogram the RADs in physical proximity to one another to correspond tothe three sectors of a triple sector set to increase the number ofsofter handoffs while decreasing the number of soft handoffs systemwide. Thus the flexibility and other advantages of the system aremaintained while further decreasing the initial cost of the systemimplementation.

There are many obvious variations to the present invention as presentedincluding simple architectural changes. The previous description of thepreferred embodiments is provided to enable any person skilled in theart to make or use the present invention. The various modifications tothese embodiments will be readily apparent to those skilled in the art,and the generic principles defined herein may be applied to otherembodiments without the use of the inventive faculty. Thus, the presentinvention is not intended to be limited to the embodiments shown hereinbut is to be accorded the widest scope consistent with the principlesand novel features disclosed herein.

We claim:
 1. An apparatus for providing a communication coverage areasthroughout a communication system comprising a cable television plantcomprising:a series of radio antenna devices (RADs) spaced along a cableeach of said series of RADs having a cable input and a cable output anda wireless input and a wireless output, wherein each of said series ofRADs receives input forward link communication signals and a RADreference signal from said cable through said cable input and providesoutput forward link communication signals through said wireless outputand receives input reverse link communication signals through saidwireless input and provides output reverse link communication signal andupstream gain reference signal through said cable output; and a headendprocessor coupled to said cable having a base station, said base stationhaving a set of demodulation elements programmably coupled to at leastone of a plurality of said series of RADs; wherein said RAD referencesignal has an absolute value dependent upon a loss between said headendprocessor and each one of said series of RADs and wherein each one ofsaid series of RADs uses said absolute value of said RAD referencesignal to set a power level of said output forward link communicationsignals.